1. Field of the Invention
The present invention relates to a semiconductor light emitting device, and more particularly to a flip-chip light emitting diode package structure.
2. Description of the Related Art
Light Emitting Diode (LED), fabricated with a semiconductor material of the Group III–V compound, can generate light, ranging from IR (infrared) to UV (ultraviolet). Recently, because of the development of the GaN blue/green LED, full color diode display and the other application can be implemented.
A LED device is basically formed with a P-type or an N-type epitaxial layer of the Group III–V compound and an active layer, i.e. a emitting layer. The efficiency of the LED device depends on the internal quantum efficiency of the active layer and the light extraction efficiency of the device. The quantum efficiency can be improved by changing the epitaxial layer structure and the quality of the epitaxial layer. The improvement of the light extraction efficiency can be achieved by reducing the reflection in the diode.
Traditionally, the electrodes of the GaN/sapphire LED are on the same surface. Because the electrodes block light, the GaN/sapphire LED usually uses a flip-chip package structure so that the light emits through the transparent sapphire substrate. Reflective layer is also formed on the epitaxial layer for reflecting most of the light to another side of the electrodes. Another advantage of the flip-chip package structure is that when an appropriate surmount, such as, an aluminum nitride submount, is applied, the thermal dispersion of the device can be improved under a high current operation. Therefore, the light extraction efficiency can be improved and the quantum efficiency of the active layer will not be degraded resulting from the thermal problem.
FIG. 1A is a schematic cross-sectional view showing a prior art flip-chip LED package structure. Referring to FIG. 1A, the package structure comprises a submount 100 and a LED chip 102, wherein the submount 100 includes bonding pads 104 and the LED chip 102 has bumps 106 thereon. When the LED chip 102 is flipped and disposed on the submount 100, the LED chip 102 electrically connects with the bonding pads 104 of the submount 100 via the bumps 106.
FIG. 1B is a schematic cross-sectional view showing a prior art structure of a flip-chip LED package structure on a circuit board. Referring to FIG. 1B, the flip-chip LED package structure is disposed on the circuit board 108 by wire bonding thereby connecting the conductive wire 112 with the bonding pads 104 and with the electrodes 110 of the circuit board 108. Therefore, the LED chip 102 electrically connects with the circuits of the circuit board 108 via the bumps 106 and the conductive wire 112.
However, because of the shrinkage of the width of the conductive wire 112, the conductive wire 112 becomes fragile and is easily broken during the process. The manufacturing cost thereby increases. Moreover, because a plurality of LED package structures is disposed on the board 108, multiple wire bonding are required and the cost is increased.
In addition, in a flip-chip LED package structure, the LED chip 102 is flipped on the submount 100 for electrically connecting therewith by the bumps 106. Therefore, the size of the prior art flip-chip LED package structure is big.